U.S. patent number 5,816,093 [Application Number 08/809,682] was granted by the patent office on 1998-10-06 for method and tool for forming a tapered hole in a cylindrical work by punching extruding.
This patent grant is currently assigned to Nitto Kohki Co., Ltd.. Invention is credited to Haruo Kubo, Hirosato Takeuchi, Shigeru Yasuda.
United States Patent |
5,816,093 |
Takeuchi , et al. |
October 6, 1998 |
Method and tool for forming a tapered hole in a cylindrical work by
punching extruding
Abstract
This invention provides a forming method capable of forming
tapered through holes at once with a single pressing operation. A
hole is formed in a work with a piercing punch 1 mounted on a press
by using a small-diameter punching portion 1a formed on the distal
end of the punch 1. A hole 11 formed at this time has a section
with an open lower end portion by pressing. By using this hole 11
as a guide, a tapering portion 1b having a diameter slightly larger
than the diameter of this hole and a tapered surface T forms a
tapered surface on the inner surface of the hole 11 in accordance
with plastic working. A "burr 3a" is formed on the edge of the hole
11 by this plastic working. Formation of this "burr 3a" is
prevented with a pressure portion 1c formed on the piercing punch
1. When the above process is performed in a single pressing
operation, a plurality of tapered through holes can be formed
easily.
Inventors: |
Takeuchi; Hirosato (Tokyo,
JP), Yasuda; Shigeru (Tokyo, JP), Kubo;
Haruo (Tokyo, JP) |
Assignee: |
Nitto Kohki Co., Ltd.
(JP)
|
Family
ID: |
26510974 |
Appl.
No.: |
08/809,682 |
Filed: |
June 25, 1997 |
PCT
Filed: |
September 27, 1995 |
PCT No.: |
PCT/JP95/01949 |
371
Date: |
June 25, 1997 |
102(e)
Date: |
June 25, 1997 |
PCT
Pub. No.: |
WO96/09904 |
PCT
Pub. Date: |
April 04, 1996 |
Foreign Application Priority Data
|
|
|
|
|
Sep 29, 1994 [JP] |
|
|
6-234811 |
Aug 3, 1995 [JP] |
|
|
7-198435 |
|
Current U.S.
Class: |
72/327; 72/325;
83/686; 83/54; 72/335 |
Current CPC
Class: |
B23P
9/025 (20130101); B21C 37/28 (20130101); B21K
21/16 (20130101); B21C 37/298 (20130101); B21K
1/00 (20130101); Y10T 83/0596 (20150401); Y10T
83/9428 (20150401) |
Current International
Class: |
B21C
37/28 (20060101); B21C 37/29 (20060101); B21K
1/00 (20060101); B21C 37/15 (20060101); B21D
028/14 (); B21D 028/28 () |
Field of
Search: |
;72/335,327,333,328
;83/54,686 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
53-2437 |
|
Jan 1978 |
|
JP |
|
56-77028 |
|
Jun 1981 |
|
JP |
|
146428 |
|
Sep 1982 |
|
JP |
|
70930 |
|
Apr 1983 |
|
JP |
|
59-174233 |
|
Oct 1984 |
|
JP |
|
63-95623 |
|
Jun 1988 |
|
JP |
|
1367639 |
|
Sep 1974 |
|
GB |
|
Other References
Press Working Handbook dated Oct. 25, 1975. .
Press Punching and Die Design dated Jan. 15, 1965..
|
Primary Examiner: Crane; Daniel C.
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
We claim:
1. A method for pressing to form a tapered hole (27) radially
extending in a cylindrical work (3) and tapered toward an inner
circumferential side of the work, comprising the following steps
of
fitting the work (3) on a sleeve-like die (2) having a die hole
(2a) on a circumferential wall portion thereof,
punching, in the work (3), a through hole having a diameter
increasing toward said inner circumferential side of the work by
using a cylindrical punching portion (1a) formed at a distal end
portion of a movable punch (1) along an axial direction of the die
hole (2a) and slightly smaller in diameter than the die hole
(2a),
extruding a material of a peripheral portion of the through hole
from an outer circumferential side of the work to the inner
circumferential side by a tapering portion (1b) formed on said
punch (1) and having a tapered surface (T) whose diameter increases
from a diameter equal to that of said punching portion (1a) to a
diameter larger than that of the die hole (2a), and
forming a surface on an inner surface of the through hole, tapered
toward the inner circumferential side of the work (3) by using the
tapered surface (T) so that said surface increases in diameter from
a point adjacent the inner circumferential side of said work
towards said outer circumferential side.
2. A method according to claim 1, wherein when a material of a
peripheral portion of the through hole is extruded from an outer
circumferential side to the inner circumferential side, a
peripheral edge of the through hole is pressed by a pressure
portion (1c) disposed near said tapering portion (1b) on a side
remote from said punching portion (1a) and having a diameter larger
than that of said tapering portion, thereby preventing a burr of
the material of the work (3).
3. An apparatus for pressing to form a tapered hole (27) radially
extending in a cylindrical work (3) and tapered toward an inner
circumferential surface of the work, comprising
a die means (2, 40) having a mounting surface corresponding to the
inner circumferential surface of the work and at least one die hole
(2a, 44) open to said mounting surface, said mounting surface unit
supporting an inner circumferential surface of the work (3),
and
a punch (1) movable along an axis of the die hole (2a, 44),
said punch including a punching portion (1a) formed to have a
diameter smaller than that of the die hole (2a) and cooperating
with the die hole to form a through hole whose diameter increases
on the inner circumferential side of the work (3), and a tapering
portion (1b), having a tapered surface (T) whose diameter increases
from a diameter equal to said punching portion (1a) to a diameter
larger than that of the die hole (2a) in a direction remote from
said punching portion (1a), for extruding a material of a
peripheral portion of the through hole from an outer
circumferential side of the work to the inner circumferential side
such that a tapered surface is formed which increases in diameter
from a point adjacent the inner circumferential side of said work
toward said outer circumferential side, and said punching portion
and said tapering portion being formed in an order named from a
distal end side.
4. An apparatus according to claim 3, wherein said punch (1) has a
pressure portion (1c) disposed near said tapering portion (1b) on a
side remote from said punching portion (1a) and having a diameter
larger than that of said tapering portion, said pressure portion
preventing a burr of a material of the through hole when said
tapering portion (1b) extrudes the material of the peripheral
portion of the through hole from an outer circumferential side to
the inner circumferential side.
5. An apparatus according to claim 3, wherein said die unit
comprises a plurality of dies (40) which are arranged along a
circumferential direction of an inner circumferential surface of
the work (3) and each of which has one die hole (44), and a press
member (47) disposed to be surrounded by said plurality of dies
(40) to urge said mounting surface (45) of each die (40) against
said inner circumferential surface of the work (3), thereby
eliminating a gap between said each mounting surface (45) and the
work (3).
6. An apparatus according to claim 5, wherein said punch (1)
comprises a punch main body having said punching portion (1a) and
said tapering portion (1b), and a slide member (50) free to be
accommodated on an outer surface of said punch main body, said
pressure portion being formed on said slide member.
Description
This application is a 371 of PCT/JP95/01949, filed Sep. 27,
1995.
TECHNICAL FIELD
The present invention relates to a method for forming a tapered
through hole in a work by pressing and a tool therefor, and, more
specifically, in a pipe joint in which a plug and a socket can be
locked with each other by utilizing, e.g., a locking ball, to a
method for forming a tapered hole serving to hold a locking ball
formed on a socket side by pressing and a hole forming tool
therefor.
BACKGROUND ART
A locking mechanism used in a conventional pipe joint will be
described with reference to the accompanying drawings. FIG. 9 is a
sectional view of the pipe joint.
Referring to FIG. 9, the pipe joint comprises a socket 20 and a
plug 30. The plug 30, having a communicating hole 33, has a
large-diameter portion having an outer circumferential groove 31 to
engage with locking balls (to be described later) provided on the
socket 20 side, and a small-diameter portion 32 on its end that can
be freely inserted into the socket.
The socket 20 having a communicating hole 26 has a front cylinder
21 in which the plug 30 is to be inserted, and a rear cylinder 21'
to be connected to the front cylinder 21 with a screw 25. A packing
22 is disposed between the front cylinder 21 and the rear cylinder
21', and a valve body 24 biased by the biasing force of a spring 23
toward the packing 22 is disposed. When the plug 30 is not inserted
in the socket, this valve body 24 abuts against the packing 22 with
the biasing force of the spring 23 to shut off the communicating
hole 26. Tapered through holes 27 are formed in the front cylinder
21 equidistantly in the circumferential direction to extend in the
radial direction, and locking balls 28 are fitted in the tapered
through holes 27 such that their spherical portions project over
the inner surface of the front cylinder 21 to engage in the outer
circumferential groove 31 of the plug 30. An operation sleeve 29
elastically biased by a spring 29a is fitted on the outer
circumferential surface of the front cylinder 21, and a pressure
surface 29b for pressing the locking balls 28 toward the center is
formed on the sleeve 29.
When the operation sleeve 29 is moved to the right in FIG. 9
against the biasing force of the spring 29a, inserting the plug 30
into the socket 20 causes the locking balls 28 arranged in the
front cylinder 21 to project into the outer circumferential groove
31 formed in the plug 30. Simultaneously, the valve body 23 is also
pushed to the right in FIG. 9 by the distal end of the plug 30 to
open the flow channel, thereby causing the communicating holes 26
and 30 of the socket and plug to communicate with each other. While
the locking balls 28 engage in the outer circumferential groove 31,
when the operation sleeve 29 is released, the sleeve is returned to
the position shown in FIG. 9 by the biasing force of the spring
29a, and the locking balls. 28 are pushed inward in the radial
direction by the pressure surface 29b of the operation sleeve 29 to
maintain engagement with the outer circumferential groove 31.
As described above, in the conventional pipe joint, when connecting
a plug and a socket, a locking mechanism utilizing locking balls is
employed. The locking balls 28 are generally accommodated in the
tapered through holes 27 formed in the socket, as described above.
Therefore, the locking balls 28 will not come off toward the center
of the front cylinder 21 due to the effect of the tapered through
holes 27 when, e.g., assembling the socket.
The tapered through holes 27 formed in the front cylinder 21 are
usually located at positions equally dividing the outer
circumference of the front cylinder into a plurality of portions.
Conventionally, to form these tapered through holes, a boring
machine, e.g., a drilling machine, is used while indexing the
positions on the outer circumference. Holes are formed one by one
by a taper drill, and are finished by a reamer.
However, to form tapered through holes one by one by using the
taper drill and the reamer is very cumbersome. As the service life
of the taper drill and the reamer is comparatively short, the
number of times of exchanging the drill and reamer increases, and
accordingly the size control is cumbersome.
DISCLOSURE OF INVENTION
It is, therefore, an object of the present invention to provide a
tapered through hole forming method capable of forming tapered
through holes as described above at once by pressing and a tool
therefor, thus solving the problems described above. When the hole
forming method or the hole forming tool of the present invention is
employed, a plurality of tapered through holes can be formed in a
work at once by pressing. As a result, the manufacturing efficiency
can be largely improved.
In order to achieve the above object, according to the first
solution employed by the present invention, there is provided a
hole forming method for forming a tapered through hole in a work by
pressing, characterized by fitting and fixing the work on an outer
circumferential surface of a cylindrical sleeve having a hole for
punching and serving as a die, performing punching to form a
punched hole in the work with a first punch having a smaller
diameter than that of the hole of the die, and thereafter moving a
second punch in this hole by using the punched hole as a guide,
thereby performing plastic working for the punched hole into a
tapered through hole with the second punch. In this working, a burr
is prevented from being formed on a peripheral edge of the hole
with a pressure portion formed on the second punch.
According to the second solution, there is provided a tapered
through hole forming tool characterized in that the tool is used
when forming a tapered through hole in a work by pressing, and a
small-diameter first punch for performing punching to form a
punched hole in the work and a second punch for performing plastic
working for the punched hole by using the punched hole as a guide,
thus forming the hole into a tapered through hole, are continuously
formed in the tool in an axial direction. A pressure portion for
preventing a burr from being formed on a peripheral edge of the
punched hole by plastic working with the second punch is formed on
the tool.
According to the third solution, there is provided a tapered
through hole forming tool and a die characterized in that the tool
and the die are used when forming a tapered through hole in a work
by pressing, a small-diameter first punch for performing punching
to form a punched hole in the work and a second punch for
performing plastic working for the hole by using the punched hole
as a guide, thus forming the hole into a tapered through hole, are
continuously formed in the tool in an axial direction, and the die
is individually formed for each tool and urged against an inner
circumferential surface of the work with a tapered member.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a view for explaining a tapered through hole forming
method according to the first embodiment of the present
invention;
FIG. 2 is an enlarged view of the main part of a piercing punch
used in forming the tapered through hole;
FIGS. 3A and 3B are respectively views for explaining formation of
the tapered through holes;
FIG. 4 is a view for explaining boring by using another piercing
punch;
FIG. 5 is an enlarged view of the main parts of a piercing punch
and a die used in a tapering method according to the second
embodiment;
FIG. 6 is a perspective view of the die shown in FIG. 5;
FIG. 7 is a partially sectional view of a piercing punch according
to the third embodiment;
FIGS. 8A and 8B are respectively views for explaining enlargement
by using the piercing punch shown in FIG. 7; and
FIG. 9 is a sectional view of a conventional pipe joint.
BEST MODE FOR CARRYING OUT THE INVENTION
A hole forming method for forming a tapered through hole according
to the first embodiment of the present invention will be described
with reference to the accompanying drawings. FIG. 1 is a view for
explaining how to form a tapered through hole in the front cylinder
of a pipe joint in accordance with this hole forming method, FIG. 2
is an enlarged front view of a piercing punch used in this hole
forming method, FIGS. 3A and 3B are views for explaining the
process of forming a tapered through hole with this piercing punch,
and FIG. 4 is a view for explaining the tapered through hole
formation with a piercing punch having no pressure portion.
Referring to FIG. 1, reference numeral 1 denotes a piercing punch
for forming a tapered through hole in a front cylinder serving as a
work; and 2, a cylindrical sleeve serving as a die. The die is
inserted in the front cylinder and cooperates with the piercing
punch 1 to form a tapered through hole. The die is fixed to one end
of a press machine non-slidably and non-rotatably with a jig (not
shown). Reference numeral 3 denotes a front cylinder serving as the
work. The front cylinder 3 is inserted in one end of the die and
held on the outer surface of the die. Reference numeral 4 denotes a
fixing member for fixing the front cylinder 3 mounted on the
die.
The piercing punch 1 is slidably held at one end of the press
machine (not shown) with a jig. While it moves forward, the
piercing punch 1 cooperates with the die 2 in a manner to be
described later to form a tapered through hole in the front
cylinder 3.
In the piercing punch 1 used for forming the tapered through hole,
a punching portion 1a (first punch), a tapering portion 1b (second
punch) having a tapered surface T, and a pressure portion 1c are
continuously formed in the axial direction in this order from the
distal end portion, as shown in FIG. 2.
The punching portion 1a has a function of forming a hole in the
work and has a circular section of the same diameter.
The tapering portion 1b having the tapered surface T has a function
of forming a tapered surface by plastic working for the inner
surface of the hole while it moves in the above punched hole as a
guide, and has the tapered surface T having a predetermined length
in the axial direction and a columnar portion continuously formed
from the upper end of the maximum-diameter portion of the tapered
surface. The columnar portion has a circular section of a diameter
larger than that of the punching portion 1a. The length of the
tapered surface T in the axial direction is determined by
considering the stroke of the punch and the like in accordance with
the shape of the required tapered through hole.
The pressure portion 1c has a function of preventing a "burr" from
being formed on the peripheral edge of the hole during plastic
working. For this purpose, the pressure portion 1c is preferably
formed conforming to the surface shape of the work. The respective
lengths of the punching portion 1a and the tapering portion 1b, and
the position of the pressure portion 1c are determined in
accordance with the thickness of the work.
The die 2 positioned at the central portion of the work has a
function of forming a hole in the work during hole formation by
cooperating with the piercing punch 1, and discharging the metal
fragments obtained by punching to the outside of the machine
through the hole. For this purpose, as shown in FIGS. 3A and 3B, a
hole 2a having a diameter slightly larger than the outer diameter
of the punching portion 1a is formed in the die 2 at a position
corresponding to the tool tip of the punch 1 described above. The
tool tip of the punching portion can be inserted in this hole
2a.The front cylinder 3 is positioned as it abuts against a stepped
portion 2b (see FIG. 1) formed on the outer surface of the die 2,
and is fixed by the fixing member 4 slidably provided coaxially
with the die.
A method of forming a tapered through hole in accordance with
pressing by using the tool described above will be described. A
plurality of tapered through holes are formed in the front cylinder
of the pipe joint (FIG. 9). When the tapered through hole forming
method of the present invention is adopted, if piercing punches are
arranged to correspond to the positions of the plurality of tapered
through holes, a plurality of tapered through holes can be formed
simultaneously with a single pressing step. Attention will be paid
to formation of one tapered through hole, and the process of
forming this through hole will be described.
FIGS. 3A and 3B are enlarged views for explaining how to form a
tapered through hole in the front cylinder as the work, in which
FIG. 3A shows a punched state with a small-diameter punching
portion, and FIG. 3B shows a state wherein the tapered surface T is
formed on the inner surface of the hole by plastic working by using
the hole formed in the work as a guide and formation of a "burr" on
the edge of the hole during plastic working is prevented.
First, the operation of forming a hole in the work 3 with the
small-diameter punching portion 1a is performed. As is known, a
hole 11 formed at this time by pressing has a section with an open
lower end portion, as shown in FIG. 3A.
Subsequently, as shown in FIG. 3B, by using the hole 11 as a guide,
plastic working is performed with the tapering portion 1b having
the tapered surface T and a diameter slightly larger than the
diameter of the hole. By this plastic working, the tapered surface
T is formed on the inner surface of the hole 11, as shown in FIG.
3B. The axial length of the tapered surface T formed on the inner
surface of the hole 11 at this time can be freely changed by
changing the tapered surface T formed on the piercing punch.
Along with this plastic working, a "burr 3a (see the broken line in
FIG. 3B)" is formed on the edge of the hole 11 by deformation of
the work. Formation of this "burr 3a" must be prevented. For this
purpose, the piercing punch 1 of the present invention has the
pressure portion 1c for preventing formation of the "burr 3a". Even
if a "burr" is formed by plastic working, the pressure portion 1c
formed on the upper portion of the tapering portion 1b having the
tapered surface T as shown in FIG. 3B can press the peripheral edge
of the hole 11. It is preferable that the pressure portion 1c that
prevents formation of the "burr 3a" have a shape matching the shape
of the outer surface of the work (if the outer surface is a curved
surface, a shape matching this curved surface). In this embodiment,
the piercing punch 1 having the flat pressure portion 1c is
used.
When tapering described above is performed, the "burr 3a" may be
formed, and sometimes the material of the front cylinder 3
plastically deforms to enter a small gap between the die 2 and the
front cylinder 3, and further a small gap 5 between the punch 1 and
the die 2, thus forming a "flush". This "flush" is usually sheared
by a corner portion 6 of the die 2 when removing the front cylinder
3 from the die 2. In a state wherein the flush is not sufficiently
sheared but remains, when the front cylinder 3 is assembled as a
pipe joint, this "flush" hinders assembly of the pipe joint. For
this reason, it is also necessary to form the corner portion 6 more
sharply so that the "flush" can be completely cut off with the
corner portion 6 of the die 2.
The second embodiment will be described with reference to FIG. 5.
The second embodiment is related to a die 2, and is characterized
in that the die 2 is individually provided for each hole formed in
a front cylinder 3 and that each die is constituted by a tapered
member 47 that strongly urges the die against the inner
circumferential surface of the front cylinder 3 in order to prevent
formation of the "flush" described above.
More specifically, referring to FIG. 5, reference numeral 40
denotes a die. The die 40 is arranged for each of holes formed in
the front cylinder 3 at positions equally dividing the entire
circumference of the front cylinder 3 into four. As shown in FIG.
6, each die 40 has a U shape when seen from the side. A hole 42 is
formed in one side 41 of the U shape to slidably hold a piercing
punch 1, and a hole 44 is formed in the other side 43 of the U
shape to cooperate with the piercing punch 1 in order to form a
hole in the front cylinder 3. An inner side surface 45 of the other
side 43 has a shape matching the inner circumferential surface of
the front cylinder 3 serving as a work (in this embodiment, as the
inner circumferential surface is circular, the inner side surface
45 is circular to match it). A tapered surface 46 is formed in the
outer side surface of the other side 43 to correspond to a tapered
member 47 (see FIG. 5) that eliminates the gap formed between the
die 40 and the front cylinder 3 when the die 40 is strongly urged
against the front cylinder. In FIG. 5, reference numeral 4 denotes
a fixing member having the same structure as that of the first
embodiment described above.
To form a tapered through hole in the front cylinder 3 serving as
the work by using this die, first, while the front cylinder 3 is
fixed with the fixing member 4, the die 40 is positioned and
arranged with respect to the front cylinder 3 to correspond to the
piercing punch, and the die 40 is urged against and fixed on the
front cylinder 3 while pushing in the tapered member. While the die
40 is fixed in this manner, the piercing punch 1 is operated, so
that a tapered hole can be formed in the front cylinder 3 in the
same manner as in the first embodiment. At this time, since the die
40 is strongly urged against the front cylinder 3 by the tapered
member 47, the gap between the die 40 and the front cylinder 3
disappears, and formation of a flush can therefore be
minimized.
In this embodiment, the die 40 is individually arranged for each
tapered hole. However, a plurality of collet chuck-like dice in
which the respective dice are separated by slits can be employed
instead.
The third embodiment will be described with reference to FIG. 7 and
FIGS. 8A and 8B. The third embodiment is related to a piercing
punch 1, and is characterized in that a pressure portion 1c of the
piercing punch is formed separately from the piercing punch 1.
Referring to FIG. 7, in the piercing punch 1 used for forming a
tapered through hole, a punching portion 1a (first punch) and a
tapering portion 1b (second punch) having a tapered surface are
continuously formed in the punch body in this order from the distal
end portion, as shown in FIG. 7, and a pressure portion 50 is
slidably formed on the outer circumferential surface of the punch
body.
A method for forming a tapered through hole with this piercing
punch will be described. FIG. 8A shows a punched state with the
small-diameter punching portion, and FIG. 8B shows a state wherein
a tapered surface is formed on the inner surface of the hole of the
work in accordance with plastic working by using this hole as a
guide and thereafter a "burr" formed on the outer periphery of the
hole during plastic working is pressed with the pressure portion
50.
An operation of forming a hole in the work with the punching
portion 1a is performed. As is known, a hole 11 formed at this time
by pressing has a section with an enlarged lower end portion, as
shown in FIG. 8A.
Subsequently, as shown in FIG. 8B, by using the hole 11 as a guide,
the tapering portion 1b having a tapered surface T and a diameter
slightly larger than the diameter of the hole is moved, thus
performing plastic working. By this plastic working, a tapered
surface is formed on the inner surface of the hole 11, as shown in
FIG. 8B. The axial length of the tapered surface formed on the
inner surface of the hole 11 at this time can be freely changed by
changing the tapered surface T formed on the piercing punch.
Along with plastic working, a "burr 3a (see the broken line in FIG.
8B)" or a "flush" is formed on the edge of the hole 11 by
deformation of the work, as described above. These "burr" and
"flush" are treated as required in the same manner as in the above
embodiments.
The other arrangements of the third embodiment are identical to
those of the first embodiment.
As described above, in the present invention, punching, plastic
working, and pressing can be performed by pressing with a single
piercing punch. Thus, when compared to the conventional operation
of forming holes one by one by using a taper drill and a reamer,
the efficiency can be improved very remarkably.
In the above embodiments, a method for forming a tapered through
hole by pressing and a tool used for this method have been
described. However, even if punching, plastic working, and pressing
are performed with different tools, the same effect as described
above can be obtained. In this case, a guide portion having a
diameter equal to the outer diameter of the punching portion of the
hole forming tool may be formed in the distal end of a tapered
surface that causes plastic deformation. As shown in FIG. 4, a
tapered through may be formed in the front cylinder with a piercing
punch having no pressure portion, and thereafter a "burr" or
"flush" formed on the edge of the hole may be removed by machining.
Furthermore, pressing becomes unnecessary depending on the
clearance between the outer diameter of the front cylinder of the
pipe joint and the inner diameter of the sleeve 29. Regarding
tools, punching and plastic working may be performed with different
tools. The present invention is not limited to formation of the
tapered through hole of a pipe joint but can be applied to
formation of various types of tapered through holes. The present
invention can be practiced in various other forms without departing
from its spirit or major features. It is to be understood that the
invention is not limited to the illustrative embodiments described
above.
INDUSTRIAL APPLICABILITY
As has been described above in detail, according to the present
invention, since a tapered through hole can be formed by pressing,
the punching efficiency can be improved greatly. If this tapered
through hole forming method is employed, a plurality of tapered
through holes can be formed simultaneously with a single pressing
step by arranging punches in accordance with the positions of the
plurality of tapered through holes. The hole positions need not be
indexed unlike in the conventional case. If the hole forming tool
of the present invention is used, a drilling operation with a taper
drill, reaming, and the like can be made unnecessary. When compared
to the drilling operation with a conventional taper drill, size
management accompanying exchange of drills and reamers becomes
unnecessary, and a through hole having a highly precise tapered
shape can be formed. Also, a "burr" and "flush" formed in hole
forming can be minimized in the present invention, and assembly of
a pipe joint can be performed smoothly, leading to excellent
effects.
* * * * *